There is mounting evidence that ecosystem response to certain types or magnitudes of extrinsic pressures (climate, human impacts, etc.) is often abrupt and non-linear, leading to a significant reorganization of system properties and processes.
These ecosystem changes are known as regime shifts (Scheffer et al. 2001). Such non-linear responses are often initiated by qualitative changes in the structure or function of the ecosystem, and are so fundamental that the impacted ecosystems respond to new pressures in completely different manners than the original ecosystem did (May 1977). Regime shifts arise, for instance, from the introduction of alien species or the loss of key species in the ecosystems. These changes can result in alterations of the most basic ecosystem parameters, including food-web structure, the flow of organic matter and nutrients through the ecosystem, or the patterns of space occupation, leading to a cascade of changes in the ecosystem. Climate drives both community structure and key organismal functions, so it is hardly surprising that regime shifts identified from marine ecosystems are often linked to climate (Cushing 1982, Steele 2004).
 Figure 1. IPCC projections for regional temperature increase for the end of the century.
The term ‘‘tipping point’’ commonly refers to a critical threshold at which minor perturbations can qualitatively alter the state or development of a system (Lenton et al. 2008). We refer here to elements to describe components of the Arctic ecosystem that may pass a tipping point. Polar, and especially Arctic, ecosystems are particularly likely to show regime shifts in response to climate change. The loss of ice represents a loss of critical habitat for ice-related species that may induce major qualitative changes in the species composition of the ecosystem (ACIA 2004, Renaud et al. 2007). Loss of ice also causes major changes in the underwater light and turbulence environment affecting primary production and other key ecosystem functions (Gradinger 1995, Wassmann 2007).
Warming of polar ecosystems allows their invasion by species opportunistically extending their latitudinal range (ACIA 2004, Berge et al. 2005, Carmack and Wassmann 2006). Temperature has a major impact on the physiological and life history traits of the organisms present (Duarte 2007). Because the Arctic is warming about three times faster than the global rate (ACIA 2004, IPCC 2007, Fig. 1), Arctic ecosystems are likely to encounter climate-driven thresholds and tipping points leading to abrupt changes much sooner than other ecosystems will. Warming of shelf waters is already leading to melting of sub sea permafrost in the East Siberian Sea, releasing methane that was formerly trapped as buried methane hydrates, and possibly having a positive feedback for climate warming (Shakhova et al. 2005). The spectacular recent acceleration of Arctic ice loss (Fig. 2, Duarte 2007) suggests that climate change has entered a new phase (Stroeve et al. 2007, Comiso et al. 2008). Indeed, the Arctic ice pack has been identified as one of the key tipping elements in the world climate system (Lenton et al. 2008), making change in the Arctic significant on a global scale. | Current models suggest that the Arctic Ocean will be largely ice-free in late summer, with a cover of mostly first-year ice in winter in 25-30 years, or even earlier (2013 has been proposed, W. Maslowski, personal communication, American Geophysical Union Fall Meeting, Dec 2007). Such extensive changes in sea ice will have unprecedented effects on Arctic ecosystems. Establishing where and when these tipping points will be reached is, therefore, a matter of urgency (ACIA 2004).
 Historical examination (ACIA 2004, Dessler and Parson 2006) has shown that such climate-induced ecosystem change, for example that reported in the waters around Greenland, have major consequences for fish catches. In a situation where the status of many living marine resources is precarious (FAO 2007), abrupt ecosystem change may have major socio-economic impacts on local communities (e.g. Inuits) dependent, both culturally and for subsistence, on these natural resources. Economic activities dependent upon marine ecosystem services, such as Arctic tourism (Stewart et al 2005) may also be vulnerable to abrupt, climate-driven changes to marine ecosystems, and face major challenges in adapting to the new conditions. In the high North, management of fisheries and marine food-web exploitation by native peoples, tourism, and oil and gas extraction is nested within larger, global-scale initiatives (e.g. Young 2002), reducing the ability of Arctic states to adapt to change. The development of a management plan for activities in the Arctic seas represents a major institutional experiment on how to address abrupt changes in the Arctic marine ecosystem.
Surprises and mistakes will occur and management must deal with that. The challenge lies in developing managerial models than can help discount anticipated risks and at the same time profit from emerging opportunities. A way of doing that is to focus on the trade offs between mitigation and adaptation/transformation strategies. Management needs to become adaptive in two ways: 1) managers would need to check indicators of approaching tipping points and adapt their strategies in case some indicator turns red. 2) At some point the alternative cost of mitigation may become too high and managers must also be prepared to adapt to the new situation after a tipping point is trespassed.
Lessons could be drawn from other management systems that have experienced major shifts in recent history (for example the Northwest Atlantic and Bering Sea areas). The success of these new models is dependent on three key factors, the availability of reliable scientific forecasts on the future changes of Arctic marine ecosystem in response to climate change, the development of regionally focused resource-use models, and communication conduits to efficiently and reliably transfer this knowledge into managerial and political frameworks.
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Work Package 6 >